1. Field of the Invention
The present invention relates to a sheet processing apparatus which is equipped in an image forming device such as a copying machine, a facsimile machine, a printer, and a multiple function processing machine and subjects a bundle of sheets such as recoding sheets for recording image information of an original to the binding process by a staple, and the like.
2. Description of the Related Art
In a sheet processing apparatus which processes a sheet formed with an image, stitch bookbinding which binds a bundle of conveyed and stacked sheets, e.g., near its center portion, in its conveying direction and folds the bound portion into two like a book for discharge. In this case, the center portion of the bundle of sheets subjected to the binding process is pushed into the nip between a pair of folding rollers by a push-out member, and the bundle of sheets is then folded by the pair of folding rollers. A sheet post-processing apparatus which presses the fold of the folded portion has been proposed (for example, see Japanese Patent Application Laid-Open No. 2003-182928).
The sheet post-processing apparatus will be schematically described with reference to FIGS. 32 and 33. A plurality of sheets stacked on a stacking portion 70 are aligned so as to be a bundle of sheets. The bundle of sheets is then stapled in the center portion in its conveying direction. The center portion of the bundle of sheets is pushed into the nip between a pair of first folding rollers 83 and 84 by a push-out plate member 82. The bundle of sheets is folded while being conveyed and is then stopped once. As shown in FIG. 34, the folded portion is nipped using a second folding roller 85 different from the first folding rollers 83 and 84. The second folding roller 85 is rotatably supported by a support shaft 851 as a bearing member. The support shaft 851 is moved along the fold in the sheet width direction orthogonally intersecting the conveying direction. Thereby, the fold is pressed by the second folding roller 85. Such creasing is performed to obtain a bundle of folded sheets P as a book subjected to the folding process. The first folding rollers 83 and 84 then start to rotate again and convey the bundle of folded sheets P to discharge it onto a tray 63.
In the case of the sheet post-processing apparatus shown in FIGS. 32 to 34, since the second folding roller 85 for pressing the fold merely runs therealong, it is hard to determine whether the fold is sufficient so that the fold can be weak. In this regard, an apparatus which presses the fold of a bundle of folded sheets by changing the running speed of the second folding roller 85 has been proposed. However even if the roller running speed is changed, the bundle of sheets instantly passes through the folding portions and there remains the problem that folding cannot be fixed.
Against the problem, there has been proposed another apparatus which reciprocates a creasing roller like the second folding roller 85 along the fold several times. In this case, the creasing roller is reciprocated several times along the fold for each bundle of folded sheets, which has low productivity and is not practical. In addition, the members of the roller reciprocating constitution are required for mechanically significant durability, which drastically increases the cost. A large stress acts also on a sheet having a low friction coefficient (p) or a thin sheet, such as a color sheet, due to roller reciprocation. Thereby, wrinkles and tears are easy to occur in the cover sheet of the bundle of folded sheets P.
There has been proposed yet another apparatus which combines a creasing roller with a punching machine as a unit and stops the operation of the unit and the creasing roller at the same time at punching (for example, see JP-A No. 2005-212991). In this case, however, the creasing roller is stopped for punching and the problem cannot be solved from the object of pressing the fold of a bundle of folded sheets.
Any of the related art sheet processing apparatuses cannot solve the problem that the bundle of folded sheets P whose fold is weak is swelled from the fold, resulting in deterioration of the appearance or look as a book. When the fold properties of the fold are week and low, and a plurality of processed bundles of sheets are stacked, the next bundle of sheets slips into a head bundle of sheets, which is significantly inferior in stacking capacity (see FIG. 31). Due to the slipping of the bundle of sheets, jamming is caused during conveyance in the sheet processing apparatus and the number of bundles of sheets made is likely to be miscounted. Therefore a new problem of affecting operability arises.
Accordingly, an object of the present invention is to provide a sheet processing apparatus, when a bundle of sheets subjected to the binding process is folded into two to make a book, for pressing the fold so as to improve its look.